package com.xuecheng.base.utils;

import java.util.Random;

/**
 * snow flow .
 *
 */
public final class IdWorkerUtils {

	private static final Random RANDOM = new Random();

	private static final long WORKER_ID_BITS = 5L;

	private static final long DATACENTERIDBITS = 5L;

	private static final long MAX_WORKER_ID = ~(-1L << WORKER_ID_BITS);

	private static final long MAX_DATACENTER_ID = ~(-1L << DATACENTERIDBITS);

	private static final long SEQUENCE_BITS = 12L;

	private static final long WORKER_ID_SHIFT = SEQUENCE_BITS;

	private static final long DATACENTER_ID_SHIFT = SEQUENCE_BITS + WORKER_ID_BITS;

	private static final long TIMESTAMP_LEFT_SHIFT = SEQUENCE_BITS + WORKER_ID_BITS + DATACENTERIDBITS;

	private static final long SEQUENCE_MASK = ~(-1L << SEQUENCE_BITS);

	private static final IdWorkerUtils ID_WORKER_UTILS = new IdWorkerUtils();

	private long workerId;

	private long datacenterId;

	private long idepoch;

	private long sequence = '0';

	private long lastTimestamp = -1L;

	private IdWorkerUtils() {
		this(RANDOM.nextInt((int) MAX_WORKER_ID), RANDOM.nextInt((int) MAX_DATACENTER_ID), 1288834974657L);
	}

	private IdWorkerUtils(final long workerId, final long datacenterId, final long idepoch) {
		if (workerId > MAX_WORKER_ID || workerId < 0) {
			throw new IllegalArgumentException(String.format("worker Id can't be greater than %d or less than 0", MAX_WORKER_ID));
		}
		if (datacenterId > MAX_DATACENTER_ID || datacenterId < 0) {
			throw new IllegalArgumentException(String.format("datacenter Id can't be greater than %d or less than 0", MAX_DATACENTER_ID));
		}
		this.workerId = workerId;
		this.datacenterId = datacenterId;
		this.idepoch = idepoch;
	}

	/**
	 * Gets instance.
	 *
	 * @return the instance
	 */
	public static IdWorkerUtils getInstance() {
		return ID_WORKER_UTILS;
	}

	public synchronized long nextId() {
		long timestamp = timeGen();
		if (timestamp < lastTimestamp) {
			throw new RuntimeException(String.format("Clock moved backwards.  Refusing to generate id for %d milliseconds", lastTimestamp - timestamp));
		}
		if (lastTimestamp == timestamp) {
			sequence = (sequence + 1) & SEQUENCE_MASK;
			if (sequence == 0) {
				timestamp = tilNextMillis(lastTimestamp);
			}
		} else {
			sequence = 0L;
		}

		lastTimestamp = timestamp;

		return ((timestamp - idepoch) << TIMESTAMP_LEFT_SHIFT)
				| (datacenterId << DATACENTER_ID_SHIFT)
				| (workerId << WORKER_ID_SHIFT) | sequence;
	}

	private long tilNextMillis(final long lastTimestamp) {
		long timestamp = timeGen();
		while (timestamp <= lastTimestamp) {
			timestamp = timeGen();
		}
		return timestamp;
	}

	private long timeGen() {
		return System.currentTimeMillis();
	}

	/**
	 * Build part number string.
	 *
	 * @return the string
	 */
	public String buildPartNumber() {
		return String.valueOf(ID_WORKER_UTILS.nextId());
	}

	/**
	 * Create uuid string.
	 *
	 * @return the string
	 */
	public String createUUID() {
		return String.valueOf(ID_WORKER_UTILS.nextId());
	}

	public static void main(String[] args) {
		System.out.println(IdWorkerUtils.getInstance().nextId());
	}
}
